Structures comprising a honeycomb core impregnated with a matrix resin wherein the core is a nonwoven paper of poly(m-phenylene isophthalamide) (MPD-I) fibrids and poly(p-phenylene terephthalamide) (PPD-T) fibers is taught in Lin U.S. Pat. No. 5,137,768.
As described in the Lin patent, the honeycomb structure is prepared by cutting individual sheets from a roll of paper, applying stripes or node lines of adhesive to the sheets and laying the sheets together. The adhesive is activated to bond the layers along the stripes. The expanded honeycomb structure is formed by pulling the sheets apart to the point where the adhesive prevents further separation. It is then dipped in epoxy or phenolic resin to impregnate the paper. Lin points out that saturation of the paper by matrix resin is important to the honeycomb properties and for this reason, paper containing no more than 50 wt. percent of fibrid is employed. An excess of fibrids seals off the paper so that the striping adhesive does not adhere adequately. It also prevents the matrix resin from penetrating sufficiently to develop the desired honeycomb properties. On the other hand, too little fibrid in the sheet results in a lack of adequate toughness.